The present invention relates to a flame retardant resin composition, and more particularly, it relates to a flame retardant polyamide resin composition which are excellent in flame retardant property, mechanical properties and heat resistance, and free from bleed-out of flame retarder and mold deposits.
Flame retardant polyamide resins reinforced by adding inorganic filler thereto have been extensively used in electric parts such as power breakers, electromagnetic switches, wiring connectors and electric tools because of excellent mechanical properties thereof.
As the reinforced flame retardant polyamide resins, there have been proposed compositions prepared by blending a flame retarder such as halogen compounds, red phosphorus and magnesium hydroxide in the polyamide resin as starting material. A part of these resins have been already put into practice. However, the compositions prepared by blending halogen compounds in the polyamide resin, tend to generate corrosive decomposition gases upon molding, resulting in corrosion of molding machine or mold, or tend to cause environmental pollution due to generation of harmful gases upon incineration thereof. Also, the compositions prepared by blending magnesium hydroxide in the polyamide resin are insufficient in mechanical properties because a large amount of magnesium hydroxide must be added thereto. In addition, the compositions prepared by blending red phosphorus in the polyamide resin tend to generate harmful gases upon molding. Thus, any of the conventional polyamide resin compositions has problems upon practical use.
As flame retardant polyamide resins which are free from the above problems, there have been proposed resin compositions prepared by blending a phosphazene compound as flame retarder in the polyamide resin as starting material (refer to Japanese Patent Application Laid-Open (KOKAI) No. 51-34946). However, according to experiments made by the present inventors, it has been found that the phosphazene compound has a poor compatibility with aliphatic polyamide resins and, therefore, suffers from remarkable bleed-out.
Resin magnets prepared by blending a magnetic powder as inorganic filler in a thermoplastic resin as binder are excellent in moldability, mechanical properties and magnetic properties and, therefore, have been widely used in various applications such as motors, audio devices, OA devices, electric or electronic parts or the like. In recent years, these resin magnets have been required to show a flame retardant property for ensuring high safety.
As the thermoplastic resins presently used in the resin magnets, polyamide resins have been most extensively used because of excellent moldability, magnetic properties, mechanical properties and so on. In particular, polyamide 6 has been preferably used for this purpose. However, since the polyamide resins themselves are combustible, the addition of a flame retarder is required for imparting a flame retardant property thereto. Hitherto, as such flame retarders used for imparting a flame retardant property to the polyamide resins, there have been extensively used halogen-based flame retarders containing halogens such as bromine and chlorine. The use of the halogen-based flame retarders, however, not only causes corrosion of molding machines or molds due to generation of corrosive gases upon molding, but also generates harmful substances such as dioxin which cause environmental pollution, upon disposal and incineration of molded products containing the flame retarder.
As a result of the present inventors' earnest studies to solve the above problems, it has been found that these problems can be eliminated by using a polyamide resin composition prepared by blending a specific amount of polyphenylene ether-based resin and/or polystyrene-based resin in a polyamide resin composition containing a phosphazene compound as flame retarder. The present invention has been attained on the basis of the finding.